My daughter was born 4 months early and was very small however once we started using a feeding pump for her feedings, she quickly gained enough weight so that she was the size of her actual age vs. her developmental age. The problem? Developmentally she was very far behind (esp. in gross motor) so by the time she was big enough to outgrow the baby bathtub she wasn't anywhere near being able to sit up on her own.
This bathtub came to the rescue. One side has a sloped side for bath time "lounging" and the other side has support for sitting straight. It also comes with a newborn sling for the top however I never used it as my daughter was too old/big for that when I got the bathtub. Although it seemed awkward at first (to support the lounging there is a raised portion on the bottom) it really did work. My daughter could take her bath without needing my constant support which made it much easier to get her washed up and encourage her to play in the water.
This next bathtub comes from one of our readers - Martha. She recommends the Clean Water Infant Tub with Built-in Thermometer by 4MomsI love the concepts behind this bathtub. It has a built in thermometer so you can tell how hot/warm/cold the water is at all times. Once we get our little preemie into the bath it's often hard to remember to check the water temperature to make sure it isn't getting too cold. The other cool thing about this bathtub is that you can constantly have the dirty water flow out and clean water flow in. The water goes through the thermometer part first so you know that any water coming in is not too hold/cold. What a nice way to keep your preemie warm and clean. Thanks for the suggestion Martha!